Marking liquid

ABSTRACT

A liquid electrostatographic toner or liquid ink jet ink prepared by the steps of heating a marking particle mix of particles of a resin and a colourant blend in a carrier liquid to a temperature between about the first softening point of the resin and about the second softening point of the resin, maintaining the temperature of the heated marking particle mix for a selected period of time, cooling the marking particle mix to room temperature, and mixing the marking particle mix with high shear. The particle mix can be produced by coarse grinding in a ball mill. The resultant toner or ink has an improved Newtonian like flow behaviour, improved electrical properties, reduced sedimentation and agglomeration and significantly improved optical density and reduced background.

FIELD OF THE INVENTION

This invention relates to a marking liquids for use in printers,including liquid developers and ink jet inks.

BACKGROUND OF THE INVENTION

A non-impact printing process can be simply defined as a process whichuses an electronic, electric, or optical means to produce characters asopposed to a mechanical means. Of the non-impact printing processes,there is a group of printing methods that use electrostatic techniques.Electrostatic printing can be defined as those methods which use theinteraction of electrostatically charged marking particles and anelectric field to control the deposition of the marking particles onto asubstrate, and encompasses processes generally known as electrographic,electrophotographic, or electrostatographic printing, as well aselectrostatic ink jet printing.

Electrostatography can be a term used to describe the various non-impactprinting processes which involve the creation of a visible image by theattraction of charged imaging particles or marking particles to chargedsites present on a substrate. Such charged sites, forming what isusually termed a latent image, can be transiently supported onphotoconductors or pure dielectrics and may be rendered visible in situor be transferred to another substrate to be developed in that location.Additionally such charged sites may be the reflection of thosestructured charges existing within a permanently polarised material asin the case with ferroelectrics or other electrets.

In electrostatography the imaging particles, generally known as toner,can be of the dry type or of the liquid type. Dry powder toners havemany disadvantages. For example the performance of dry powder toners isvery susceptible to environmental conditions, influencing, for example,charge stability, and therefore giving rise to variable imageperformance. Also, the large particle size of dry powder toners is amajor contributing factor in not allowing the achievement of highlyresolved developed images. For high speed, long run printing, cost perpage is a principal consideration. In particular, the cost of fusing theimage to paper or any other desired substrate significantly contributesto the running costs of such a printer. Other objections are related tothe problem of dusting. Dust or fine or small particles of toner areprone to escape from the developer, and these deposit onto any surfaceboth within and outside the printing device, causing mechanical failureswithin the device and environmental problems outside the device. Thisproblem becomes severe when such printing devices are run at high speed.Other disadvantages include cost of the general maintenance of theprinter and cost of the dry powder toner.

It is known that latent electrostatic images can be developed withmarking particles dispersed in insulating or non-polar liquids. Thesedispersed materials are known as liquid toners or liquid developers.Liquid toner development systems are generally capable of very highimage resolution because the toner particles can safely be much smaller,normally in the range of 0.5 to 3 μm, than dry toner particles which arenormally in the range of 7 to 10 μm. Liquid toner development systemsshow impressive gray scale image density response to variations in imagecharge and achieve high levels of image density using small amounts ofliquid developer. Additionally, the systems are usually inexpensive tomanufacture and are very reliable, furthermore the liquid toners forthese systems are operationally and chemically stable thus exhibiting aparticularly long shelf-life.

Ink jet printing is a non-impact printing process that does not involvea latent image; it is a direct printing system. It is usual for an inkto be fed through a nozzle. The droplets may be produced from the nozzleeither continuously in which case the method is termed continuousprinting or they may be produced individually as required in which casethe method is termed drop on demand printing. In continuous printing anink is delivered through the nozzle at high pressure and the nozzle isperturbed at a substantially constant frequency which results in astream of droplets of constant size. By applying charge to the dropletsand using an electric field external to the nozzle selected droplets maybe deflected in their passage to the recording surface in response to asignal effecting the electric field whereby forming a pattern on therecording surface in response to the control signal. Drop on demandprinting operates by producing local pulses in the liquid in thevicinity of a small nozzle which results in a droplet of liquid beingejected from the nozzle.

In either type of jet printing the colouring material is a soluble dyecombined with binders to render the printed image more permanent. Thedisadvantage of soluble dyes is that the printed image density is nothigh enough in many applications and that the dyes fade under exposurein the environment. A further disadvantage with soluble dye materials isthat the quality of the printed image is dependent on the properties ofthe recording surface. Pigmented inks are known to produce higherdensity images than soluble dyes and are also more permanent. Pigmentsmay also be used in jet printers but the production of a dense imagerequires a high concentration of pigment material in a liquid carrier.The high concentration of pigment material affects the droplet break-upin continuous printers and results in less uniform printing. Drop ondemand printers do not have a high continuous pressure and the dropletgeneration is strongly dependent on local conditions in the nozzle,therefore the presence of pigments can block the nozzle or otherwisemodify the local nozzle conditions or block the nozzle such thatdroplets are not correctly ejected.

Electrostatic ink jet can be characterised by droplets being drawn froman orifice under the influence of an electrostatic field. This fieldacting between a valving electrode and the orifice, attracts freecharges within the ink to its surface such that a droplet is producedwhen the electrostatic pull exceeds the surface tension of the ink. Asthis technique relies on attraction of free charges, it thereforerequires that the ink be conductive.

A new electrostatic ink jet printing technology has been described inU.S. Pat. No. 6,260,954 to Lima-Marques. This process provides a meansof producing variable sized droplets that contain a high concentrationof particulate material. Specific advantages conveyed by this processinclude the ability to form droplets as small as a few micrometers whilestill using pigments as the colorant material. This is because the sizeof the droplets are controlled primarily by the voltage on an ejectionpoint plus the ability of the particles to be charged. Also the colorantmaterial is significantly concentrated in the ejected droplets.Therefore high resolution and high density images based on light andwater resistant pigments can be produced.

It will be understood by those skilled in the above described non-impactprinting art that the operational requirements for an effective liquidtoner or liquid developer and that of an ink jet ink, in particular anelectrostatic ink jet ink, can be significantly different. For thepurpose of this specification and invention, however, the usage of theterm marking liquids will be deemed to mean both liquid developers andliquid ink jet inks and in many instances, as would be understood bythose skilled in the art, specific references to liquid developers mayalso be applicable to liquid ink jet inks, in particular toelectrostatic ink jet inks.

In general, the process of production of electrostatic marking liquidscommences with a resin or a resin system which can contain a resin or acombination of resins and which may also contain a colourant, which canbe ground, extruded from a suitable mixing machine or otherwise combinedby other techniques known to the art, including means of producing aMasterbatch such as for example a twin roll mill. Additionally includedin the resin system there can be added dispersing resins, plasticisersor varnishes, as is generally known in the art.

Additionally, charge directing agents are usually included in themarking liquids to control the polarity and charge to mass ratio of thetoner particles. The colourant can be a dye which is soluble in theresin or a pigment comprising of colourant particles which are notsoluble in the resin. The resin system and colourant are then milled ina carrier liquid in which neither the resin nor the colourant issoluble, to produce a marking liquid with very fine marking particlesdistributed in it.

Liquid developers have generally utilized low viscosity liquids and lowconcentration of the solids content, that is, of marking particles.These traditional toners and associated process systems may be termedlow viscosity toner or LVT systems. Generally, LVT systems utilisetoners with low viscosities, typically 1 to 3 mPa·s. and low volumes ofsolids, typically 0.5 to 2% by weight. Maintaining a uniform dispersionof the marking particles can be difficult in a low viscosity tonersystem. The marking particles have a tendency to drift and settle in thecarrier liquid. Furthermore, low volume of solids in the toner increasesthe amount of toner required to develop a given latent image. More tonerwill have to be transferred to the photoconductor in order to providesufficient marking particles for a desired image density.

To overcome these and other known problems that can be associated withLVT systems, highly concentrated liquid toner development systemsutilising toner concentrations of up to 60% by weight and viscosities ofup to 10,000 mPa·s, and utilizing thin films, typically 1 to 40 μm, ofthe highly concentrated and viscous liquid toner have been disclosed.This system of developing electrostatic latent images with these viscousand highly concentrated liquid toner systems may be termed highviscosity toner or HVT systems. Examples of such liquid toners aredisclosed in commonly assigned U.S. Pat. No. 6,287,741 to Marko, thedisclosure of which is totally incorporated herein by reference.Examples of high viscosity, high concentration liquid developing methodsand apparatus are disclosed in commonly assigned U.S. Pat. No. 6,137,976to Itaya et al. and U.S. Pat. No. 6,167,225 to Sasaki et al., thedisclosures of which are totally incorporated herein by reference.

Many such hitherto produced marking liquids have been found to haverheologies which can have non-Newtonian flow with applied shear andhence may not have ideal flow characteristics suitable under allconditions for their ultimate intended use. Particle size distributionof the marking particles of so produced marking liquids has also beenfound to be variable. Other possible problems encountered can includepoor dispersion stability, variable electrical characteristics andgenerally variable print performance.

It is the object of this invention to provide a process for producingthese marking liquids which will overcome these problems by providing analternative ink or toner preparation method, or a post-production methodto improve the performance of prior art marking liquids and a markingliquid so produced.

BRIEF DESCRIPTION OF THE INVENTION

In one form the invention is said to reside in a liquidelectrostatographic toner or liquid ink jet ink prepared by a methodincluding the steps of,

a) preparing a resin system comprising a resin or resins with optionallya colorant,b) coarse grinding the resin system,c) milling the coarse ground resin system with a carrier liquid toproduce a liquid marking particle mix,d) heating the liquid marking particle mix to a temperature about orgreater than the first softening point of the resin system of themarking particle mix to less than about the second softening point ofthe resin system,e) maintaining the temperature of the heated marking particle mix for aselected period of time,f) cooling the marking particle mix to room temperature, andg) mixing the marking particle mix with high shear.

Preferably the resin system comprises;

-   -   0 to 60% of the colourant; and    -   resin or resins to 100%

Preferably the resin system further comprises a plasticiser in a rangeof from 0 to 20%.

Preferably the liquid electrostatographic toner or liquid ink jet inkcomprises:

-   -   1 to 60 percent marking particle mix by weight,    -   0.01 to 5 percent charge control agent,    -   0.1 to 20 percent dispersion agent, and    -   carrier liquid to 100 percent.

Preferably the selected period of time is from several minutes toseveral days depending upon the type of heating applied and the methodof applying that heat.

Preferably the heating is provided by convection, conduction orradiation.

The plasticiser can be selected from the group comprising sulfonamides,adipates, sebacates and phthalates.

Preferably the step of milling the resin system includes milling withadditives selected from one or both of the group comprising chargecontrol agents and dispersion agents.

The resin can be selected from one or more of the group comprising ethylcellulose, oil modified alkyd resin, acrylic ester resin, methacrylicester resin, polystyrene, silicone-acryl copolymer, silicone resin,silicone-(meth)acryl copolymer, block polymer or graft polymer,polyolefin copolymer, poly(vinyl chloride) resin, chlorinatedpolypropylene, polyamide resin, coumarone-indene resin, rosin-modifiedresin, alkylphenol-modified xylene resin, synthetic polyesters;polypropylene or modified polypropylene; alkylated poly vinylpyrrolidones; natural waxes, montan wax, candelilla wax, sugar cane wax,beeswax; natural resins, ester gum and hardened rosin;natural-resin-modified cured resins, natural resin-modified maleic acidresins, natural resin-modified phenol resins, natural resin-modifiedpolyester resins, natural resin-modified pentaerythritol resins andepoxy resins.

The colourant when present can be selected from one or more of inorganicpigments selected from carbon blacks, silica, alumina, titanium dioxide,magnetic iron oxide, or organic pigments selected from phthalocyanineblue, alkali and reflex blue, phthalocyanine green, diarylide yellow,arylamide yellow, azo and diazo yellow, azo red, rubine toner,quinacridone red, basic dye complexes, lake red, or fluorescent pigmentsand dyestuffs selected from basic dyes and spirit soluble dyes orcombinations thereof.

The carrier liquid can be selected from the group comprisingisoparaffinic-hydrocarbons, silicone fluids of straight chainedconfiguration, silicone fluids of cyclic configuration, silicone fluidof branched configuration, vegetable oils, synthetic oils or polybutenesor blends thereof.

The charge control agent can be selected from the group comprisingmetallic soaps, fatty acids, lecithin, organic phosphorus compounds,succinimides and sulphosuccinates.

The dispersion agent can be selected from the group comprising polymerichyperdispersants, amino-silicones, polymeric petroleum additives,polymeric oil additives and multi-functional pigment dispersing agents.

In an alternative form the invention comprises a liquidelectrostatographic toner or liquid ink jet ink prepared by a methodincluding the steps of,

a) preparing a resin system comprising a resin or resins with a colorantand a plasticiser, the resin system comprising;

-   -   1 to 60% of the colourant;    -   1 to 20% plasticiser; and    -   resin or resins to 100%        b) coarse grinding the resin system,        c) milling the coarse ground resin system with a carrier liquid        to produce a liquid marking particle mix,        d) heating the liquid marking particle mix to a temperature        about or greater than the first softening point of the resin        system of the marking particle mix to less than about the second        softening point of the resin system,        e) maintaining the temperature of the heated marking particle        mix for a selected period of time,        f) cooling the marking particle mix to room temperature, and        g) mixing the marking particle mix with high shear;        wherein the liquid electrostatographic toner or liquid ink jet        ink comprises;    -   1 to 60 percent marking particle mix by weight,    -   0.01 to 5 percent charge control agent,    -   0.1 to 20 percent dispersion agent, and    -   carrier liquid to 100 percent.

The first softening point is defined as the temperature where themacromolecular structure of the resin begins to relax. The secondsoftening point is defined as the temperature where the resin begins toflow as it approaches its melting transition. The first and secondsoftening points can be measured with a Thermal Mechanical Analyser(TMA). The first and second softening points from a TMA are oftencomparable to Tg (glass transition) and Tm (melting point) respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription taken with the accompanying drawings in which:

FIG. 1 is a graph illustrating the rheology of Example 1 with notreatment;

FIG. 2 is a graph illustrating the rheology of Example 1 afterconvection treatment;

FIG. 3 is a graph illustrating the rheology of Example 1 after microwavetreatment;

FIG. 4 is a graph illustrating the rheology of Example 2 with notreatment;

FIG. 5 is a graph illustrating the rheology of Example 2 afterconvection treatment;

FIG. 6 is a graph illustrating the rheology of Example 2 after microwavetreatment;

FIG. 7 is a graph illustrating the rheology of Example 3 with notreatment;

FIG. 8 is a graph illustrating the rheology of Example 3 afterconvection treatment;

FIG. 9 is a graph illustrating the rheology of Example 3 after microwavetreatment;

FIG. 10 is a graph illustrating the rheology of Example 4 with notreatment;

FIG. 11 is a graph illustrating the rheology of Example 4 afterconvection treatment;

FIG. 12 is a graph illustrating the rheology of Example 4 aftermicrowave treatment;

FIG. 13 is a graph illustrating the rheology of Example 5 with notreatment;

FIG. 14 is a graph illustrating the rheology of Example 5 afterconvection treatment; and

FIG. 15 is a graph illustrating the rheology of Example 5 aftermicrowave treatment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In this specification, the invention will be discussed particularly inrelation to the use of the invention for the production of liquidtoners, including so-called high viscosity high concentration liquidtoners, for electrostatic printing applications. It would be understoodby those skilled in the art that the methods described herein are alsoapplicable to the production and processing of ink jet inks, includinginks suitable for electrostatic type ink jet printers.

In general, a liquid developer or toner for electrostatography isprepared by dispersing an inorganic or organic colourant in a carrierliquid. The liquid developer should be stable, not only in terms ofsuspension stability, but also of electrical charge. As such numerousadditional components can be additionally integrated into the developerto achieve liquid developers that exhibit reproducible high qualityimages.

In such developers, it has been recognised that certain properties ofthe carrier liquid are mandatory requirements for the effectivefunctioning of a conventional electrostatographic liquid developmentprocess. The mandatory requirements include low electrical conductivitybut other requirements have also become obvious, such as the need forlow toxicity, increased fire safety, low solvent power, low odour etc.For these reasons, isoparaffinic-hydrocarbons such as the Isopar® rangemanufactured by Exxon Mobil, the Shellsol® range manufactured by ShellChemical and the Soltrol® range manufactured by Chevron PhillipsChemical Company have become the industry standards for liquid tonercarriers.

Other carrier liquids may be used, and these may also comprise asilicone fluid of straight chained configuration, a silicone fluid ofcyclic configuration, a silicone fluid of branched configuration, or acombination thereof.

The carrier liquid may also comprise a mineral oil or white oil.

The carrier liquid may also comprise a vegetable oil. Representativeexamples of vegetable oils include soybean oil, cottonseed oil,safflower oil, sunflower oil, castor oil, linseed oil and olive oil.

The carrier liquid may also comprise a synthetic oil. Representativeexamples of synthetic oils include fatty acid esters obtained by thereaction between higher fatty acid and alcohol, and ester compoundsobtained by the reaction between higher fatty acid and ethylene glycolor glycerine.

The carrier liquid may also comprise a polybutene, a synthetichydrocarbon polymer made by the polymerisation of isobutene (also knownas “isobutylene”). Another name for polybutene is polyisobutylene.

It would be understood by those skilled in the art that blends of theabove-mentioned carrier liquids or other suitable carrier liquids couldbe used in relation to this invention.

Colourants that are insoluble in the carrier liquid may be selected upontheir particular proposed end use. Examples of marking particles includeinorganic pigments such as iron oxide, silica, alumina, titaniumdioxide, magnetic iron oxide, or organic pigments such as carbon black,phthalocyanine blue, alkali and reflex blue, phthalocyanine green,diarylide yellow, arylamide yellow, azo and diazo yellow, azo red,rubine toner, quinacridone red, basic dye complexes, lake red, orfluorescent pigments and dyestuffs such as basic dyes and spirit solubledyes, or combinations thereof. Other materials, as would be understoodby those skilled in the art, could be used as colourants.

As indicated above, the liquid developer or toner may also include anorganic or inorganic insoluble marking particle and such a markingparticle may be present in the range of 1 to 60% by weight.

The resin or combination of resins to make up the resin system may beselected from one or more of ethyl cellulose, oil modified alkyd resin,acrylic or methacrylic ester resin, polystyrene, silicone-acrylcopolymer, silicone resin, silicone-(meth)acryl copolymer, block polymeror graft polymer, polyolefin copolymer, poly(vinyl chloride) resin,chlorinated polypropylene, polyamide resin, coumarone-indene resin,rosin-modified resin, and alkylphenol-modified xylene resin, syntheticpolyesters; polypropylene or modified polypropylene; alkylated polyvinyl pyrrolidones; natural waxes such as montan wax, candelilla wax,sugar cane wax, beeswax, natural resins such as ester gum and hardenedrosin; natural-resin-modified cured resins such as naturalresin-modified maleic acid resins, natural resin-modified phenol resins,natural resin-modified polyester resins, natural resin-modifiedpentaerythritol resins, styrene acrylates and epoxy resins.

Other components such as plasticisers can also be incorporated, examplesof which are sulfonamides, adipates, sebacates and phthalates.

Additionally to affect or enhance electrostatic charge on such dispersedparticles additives known as charge directors or charge control agentsmay be included. Such materials can be metallic soaps, fatty acids,lecithin, organic phosphorus compounds, succinimides andsulphosuccinates.

The charge control agent may be present in a range of 0.01 to 5% byweight of the toner when used.

The liquid developer or toner may also include a dispersion agent whichcan be selected, for example, from the Solsperse® range of polymerichyperdispersants including 13940 made by Avecia; amino-siliconesincluding Finish® WR101 made by Wacker Chemicals; polymeric oiladditives including Plexol® made by Rohm and Haas; polymeric petroleumadditives including FOA-2® made by Dupont; multi-functional pigmentdispersion agents including Disperse Ayd 1® made by Elementis DCP Inc.

The dispersion agent may be incorporated into the liquid composition bytechniques commonly employed in the manufacture of liquid compositionssuch as ball-jar milling, attritor milling, bead milling etc. Pre-mixingtechniques involving blending the dispersion agent into the carrierliquid before the addition of marking particles and before the millingstage can also be used to incorporate the dispersion agent into theliquid developer formulation.

The dispersion agent may be present in a range of 0.1 to 20% by weightof the toner when used.

Examples of suitable liquid toner formulations include those disclosedin commonly assigned U.S. Pat. No. 5,591,557 to Lawson et al., U.S. Pat.No. 5,612,162 to Lawson et al., U.S. Pat. No. 6,174,640 to Lawson andU.S. Pat. No. 6,287,741 to Marko, the disclosures of which are totallyincorporated herein by reference.

The Applicant has surprisingly found that liquid toners manufactured asin the abovementioned disclosures will exhibit an enhanced performanceon all levels if the so produced liquid toner is post treated by heatingthe liquid toner to a temperature about or above the first softeningpoint of the resin of the liquid marking particle mix, maintaining thetemperature of the heated marking particle mix for a selected period oftime, cooling the resin to room temperature, and mixing the liquid tonerwith high shear.

The Applicant has additionally found that liquid toner performance canbe even further enhanced by matching the liquid toner resin system tothe dispersing agent and carrier liquid. The heating process can then beoptimised to the thermal characteristics of the resin system, andtherefore produce a more effective post treatment result.

The selected heating period may be from several minutes to several daysdepending upon the type of heating applied and the method of applyingthat heat. Heating can be done by convection, such as in an oven,conduction or electromagnetic radiation, such as microwave radiation.Due to the different energies of these different heating systems themethod chosen will determine the conditions required to achieve thedesired results. In some instances, however, such as in a convectionoven, it has been found that it is important that the liquid toner isevenly heated to the required temperature, and that no or minimalagitation takes place during the heating stage. The heating temperaturecan be dependent on the resin system used in the liquid tonerformulation and the Applicant has found that it should be about or justabove the first softening point of the resin or resins.

High shear mixing can be achieved with any commercially available highshear mixers. The Applicant has found that the degree of mixing requiredis dependent on the solid content of the formulation, that is, thehigher the solids content of the liquid developer the higher the energyinput requirement.

Although the exact process by which this method of preparation improvesthe desired characteristics of a liquid toner is not fully understood,the following explanation will be given but the Applicant is not boundto this explanation.

It is believed that during the heating stage when the resin is heated toabout or just above its first softening point, the structure of theresin particles begins to relax as internal stresses are released as theresin begins to transit through its glassy state, and surface tensioneffects occur such that the morphology of the toner particles assumes asmoother shape.

The action of a suitable dispersing agent in the liquid toner prior tothe treatment is useful at this point because it ensures that individualparticles of resin and colourant remain separated from one another so asthey do not agglomerate or stick together. The dispersing agent achievesthis through its strong affinity for the toner particle causing it toform a protective layer around the particle and therefore providing anadequate barrier between neighbouring resin and colourant particlesthrough steric hindrance forces and enabling the particle surface torelax and flow and thus become smoother.

It has been noted that after the heating and cooling stage, a weaklyformed gel structure can often form which is believed to be due topossible weak attraction or interaction of dispersion agent speciesresiding on the surface of one particle with that of another particle.This interaction is easily broken up by moderate shearing forces usedduring the high shear mixing stage of the process.

It has also been noted that liquid toners produced by the process of thepresent invention exhibit a more Newtonian like flow behaviour with verylittle or no yield viscosity, as can be see in FIG. 2-3, FIG. 5-6, FIG.8-9, FIG. 11-12 and FIG. 14-15; even with high solid contentformulations of up to 60% by weight solids but preferably in the rangeof 10-40% weight solids. There is also a significantly reduced highshear toner viscosity. This means that when the toners for instance areused in printing machines, the characteristic viscosity of the toner isless dependant on the speed of rollers and the like and hence has a moreeven and predictable action during use.

Smoothing of the toner particle surface results in a reduced surfacearea causing improved flow properties which can be related to themeasured viscosity change with change in shear.

The Applicant has also found improved toner stability. Depending on thetype of dispersion agent and resin system used, there can be an enhancedinteraction during the heating stage of the process between thedispersion agent and the particle and/or the reaction of the functionalgroups of specific dispersion agent materials with epoxide groups ofspecific resin system to key the dispersion agents strongly to thesurface of the toner particle resulting in improved toner dispersionstability. Increased stability may also be achieved as a result of areduced toner particle surface area such that the ratio of dispersionagent available per unit surface area of toner particle hassubstantially increased.

The Applicant has also noted improved toner electrical properties. Dueto smoothing of the toner particle surface, reduced high shear viscosityand Newtonian like flow behaviour being achieved, the charge to massratio of the toner particles increases apparently due to higheradsorption of charging and dispersing species on the toner surface alongwith increased toner mobility to give improved electrical properties tothe liquid developer.

The electrical characteristics of a liquid developer can be measuredwith a liquid toner characterization cell, of which apparatus detailsare disclosed in commonly assigned U.S. Pat. No. 6,613,209 to Ozerov,the disclosure of which is totally incorporated herein by reference.

The liquid toners prepared according to this present invention alsoexhibit improved print performance. Liquid toners prepared according tothe present invention also show substantially increased optical density,decreased background staining, higher image resolution and improvedtoner management and handling characteristics. These toner handling andmanagement characteristics include improved ability for recycling andreplenishment of toners and the general flow of the toner within aprinter.

This then generally describes the invention but to assist withunderstanding, reference will now be made to the accompanyingnon-limiting examples which show embodiments of the invention.

EXAMPLES Example 1

An extrudate 1 was prepared with the following composition:

Epikote 1001 61.5 g Antaron V220 18.5 g Irgalite Blue LGLD   20 g

The above components were blended together to form the extrudate 1using, for example, a hot-melt extruder and allowed to cool. Theextrudate 1 was then crushed to a coarse powder, ready for use in theexample.

Epikote 1001 is an epoxy resin made by Shell Chemicals, Australia.Irgalite Blue LGLD is a CI Pigment Blue 15:3 made by Ciba-Geigy, Base1Switzerland. Antaron V220 is an alkylated polyvinylpyrrolidone made byGAF/ISP Chemicals, New Jersey U.S.A.

A marking liquid of the following composition was then prepared usingthe extrudate 1:

Extrudate 1 125 g Finish WR1101  5 g DC 200 Fluid 10 cSt 370 g

Finish WR1101 is a dimethyl polysiloxane having amino-alkyl functionalgroups, made by Wacker Chemicals, Munich Germany. DC 200 10 cSt Fluid isa silicone fluid made by Dow Corning, U.S.A.

Example 2

An extrudate 2 was prepared with the following composition:

Epikote 1004 73 g Jayflex UDP  7 g Irgalite Blue LGLD 20 g

The above components were blended together to form the extrudate 2using, for example, a hot-melt extruder and allowed to cool. Theextrudate 2 was then crushed to a coarse powder, ready for use in theexample.

Epikote 1004 is an epoxy resin made by Shell Chemicals, Australia.Jayflex UDP is a phthalate plasticiser (undecyl dodecyl phthalate) madeby Exxon Mobil.

A marking liquid of the following composition was then prepared usingthe extrudate 2:

Extrudate 2 125 g Finish WR1101  5 g DC 200 Fluid 50 cSt 370 g

DC 200 50 cSt Fluid is a silicone fluid made by Dow Corning, U.S.A.

Example 3

A marking liquid of the following composition was prepared:

Solsperse 13940  10 g Marcol 82 INH 365 g Epikote 1004 100 g IrgaliteBlue LGLD  25 g

Solsperse 13940 is a dispersing agent made by Avecia. Marcol 82 INH is awhite-oil made by Exxon Mobil.

Example 4

An extrudate 3 was prepared with the following composition:

Monarch Fluffy 435 25 g Jayflex UDP  6 g Epikote 1004 69 g

The above components were blended together to form the extrudate 3using, for example, a hot-melt extruder and allowed to cool. Theextrudate 3 was then crushed to a coarse powder, ready for use in theexample.

Monarch Fluffy 435 is a carbon black, Pigment Black 7, manufactured byCabot Corporation.

An ink jet ink of the following composition was then prepared using theextrudate 3:

Extrudate 3 100 g Solsperse 13940  20 g 6% Zirconium Octoate  25 gIsopar G 355 g

6% Zirconium Octoate is a solution of zirconium octanoate in whitespirits made by Exxon Mobil. Isopar G is an isoparaffinic solvent madeby Exxon Mobil.

This Example 4 was treated with the present invention as a so producedconcentrate. For imaging tests, the so treated concentrate was thendiluted 1:5 with Isopar G prior to testing in the printing device.

Example 5

U.S. Patent Application 2003/0104304A1 to Nicholls, the disclosure ofwhich is totally incorporated herein by reference, discloses prior artliquid developers in which the liquid carrier comprises or includes apolybutene. Example 2 of the above patent application was manufacturedas disclosed in said application and then further treated using thepresent invention.

The so produced marking liquids of the above examples were prepared byadding the constituents into a ceramic ball jar containing sphericalceramic grinding media and milling for 4 days to prepare a resinoustoner or ink, or as described in the relevant prior art.

It should be understood that the quantities of raw materials in theExamples 1 to 4 can be varied dependent on the liquid developer or inkcharacteristics required and the mode of operation of the electrostaticprinter.

The thermal properties of the resin systems of the Examples are asfollows:

Example First Softening Point Second Softening Point 1 50.9° C. 87.2° C.2 45.5° C. 79.3° C. 3 61.5° C. 106.8° C.  4 50.2° C. 82.8° C. 5 44.6° C.80.7° C.

The above results were measured using a Seiko Thermal MechanicalAnalyser (TMA), Type TMA120C.

The marking liquid Examples were then divided into three batches. Twobatches of each were further treated according to the present inventionas follows:

A first batch of so produced marking liquid was placed in a suitablecontainer and subjected to heating in an oven. The marking liquid washeated in the oven at a set temperature and maintained at thattemperature for a period of 48 hours without any form of agitation.

Example Oven Temperature 1 60° C. 2 50° C. 3 70° C. 4 60° C. 5 50° C.

Heating of the marking liquids about or above the first softening pointof the resin system of the marking particle mix, causes the structure ofthe resin particles to begin to relax as internal stresses are releasedand surface tension effects occur such that the morphology of themarking particles assumes a smoother shape. After the 48 hour heatingperiod, the marking liquids were taken out of the oven and allowed tocool to room temperature. Once the marking liquids are at or near roomtemperature the marking liquids are then mixed with high shear. This wasachieved with an IKA-Werk Type SD40 Super Dispax, controlled with anIKA-Werk DS1 Controller, both manufactured by Jankel & Kunkel GmbH. Thetoners are subjected to high shear mixing with one pass through theabove mixer at a dial speed setting of 50 and a rotor-stator gap dialsetting of 1.

A second batch of each Example was treated using radiation as theheating mechanism for post treatment and was prepared by heating thebatches with microwaves. A microwave generator at 2450 MHz with variablepower capacity was used to heat the batches. The batches, consisting of100 grams of the marking liquid were heated in a Pyrex® glass cylinderto the required temperature for 1 minute, and then maintained at therequired temperature for 10 minutes. The table below illustrates theapproximate microwave power settings used for heating and maintainingthe batches at temperature.

Microwave Power Microwave Power Example Temperature (1 minute) (10minutes) 1 60° C. 250 W 40 W 2 50° C. 180 W 35 W 3 70° C. 315 W 45 W 460° C. 250 W 40 W 5 50° C. 180 W 35 W

The batches were then allowed to cool to room temperature and then mixedwith high shear as previously described.

The physical properties of particle size, rheology, mobility andmorphology of the marking liquid particle for the microwave heat treatedbatches were similar to that of the oven heated treated batches, whereparticle size was reduced, rheology became more Newtonian, mobility wasincreased and particle morphology was much smoother.

The batches both before and after the treatment by the invention werethen examined for various physical properties and for print quality byproducing print samples. The rheological data for stress versus shearrate and viscosity versus shear rate are shown in FIGS. 1 to 15.

Physical Properties Particle Size.

Characteristics measured were D[4,3] which indicates the equivalentspherical volume diameter mean and this value is biased toward largerparticles since volume is a function of the cube of the particle radius;and D[v,0.5] which indicates the volume 50% value of the distribution.This differs from D[4,3] if the volume distribution is skewed.

Results were as follows:

Microwave No Treatment Convection Treatment Treatment Example 1 D[4, 3]1.27 μm  1.10 μm 1.18 μm D[v, 0.5] 1.06 μm. 0.93 μm 0.98 μm Example 2D[4, 3] 1.95 μm  1.79 μm 1.80 μm D[v, 0.5] 1.51 μm. 1.44 μm 1.47 μmExample 3 D[4, 3] 1.42 μm  1.35 μm 1.27 μm D[v, 0.5] 0.97 μm. 0.90 μm0.89 μm Example 4 D[4, 3] 0.81 μm  0.69 μm 0.70 μm D[v, 0.5] 0.58 μm.0.52 μm 0.53 μm Example 5 D[4, 3] 1.27 μm  1.10 μm 1.18 μm D[v, 0.5]1.06 μm. 0.93 μm 0.98 μm

These results show a significant drop in particle size and a narrowerdistribution.

Particle size distribution was measured using a Malvern Mastersizer.

Viscosity

Viscosities were measured using a HAAKE RheoStress RS100. Allmeasurements were taken at 20° C. FIG. 1 of the attached drawings showsExample 1 before treatment, FIG. 2 shows Example 1 after convectiontreatment and FIG. 3 shows Example 1 after microwave treatment.

FIG. 1 illustrates that prior to the treatment, the toner wasnon-Newtonian and exhibited shear thinning, with a high shear viscosityof 92.1 mPa·s. FIG. 2 illustrates the same toner after the convectiontreatment. It now exhibits a significant reduction in non-Newtonian flowbehaviour or yield viscosity, with a high shear viscosity of 53.2 mPa·s.FIG. 3 illustrates the same toner after microwave treatment. It now alsoexhibits a significant reduction in non-Newtonian flow behaviour oryield viscosity, with a high shear viscosity of 50.7 mPa·s.

FIG. 4 of the attached drawings shows Example 2 before treatment, FIG. 5shows Example 2 after convection treatment and FIG. 6 shows Example 2after microwave treatment.

FIG. 4 illustrates that prior to the convection treatment, the toner wasnon-Newtonian and exhibited shear thinning, with a high shear viscosityof 200 mPas.

FIG. 5 illustrates the same toner after the convection treatment. It nowexhibits a significant reduction in non-Newtonian flow behaviour oryield viscosity, with a high shear viscosity of 137 mPas. FIG. 6illustrates the same toner after microwave heat treatment. It now alsoexhibits a significant reduction in non-Newtonian behaviour or yieldviscosity, with a high shear viscosity of 125 mPa·s.

FIG. 7 of the attached drawings shows Example 3 before treatment, FIG. 8shows Example 3 after convection treatment and FIG. 9 shows Example 3after microwave treatment.

FIG. 7 illustrates that prior to the convection treatment, the toner wasnon-Newtonian and exhibited shear thinning, with a high shear viscosityof 68.4 mPas. FIG. 8 illustrates the same toner after the convectiontreatment. It now exhibits a significant reduction in non-Newtonian flowbehaviour or yield viscosity, with a high shear viscosity of 64.4 mPas.FIG. 9 illustrates the same toner after microwave heat treatment. It nowalso exhibits a significant reduction in non-Newtonian behaviour oryield viscosity, with a high shear viscosity of 64.7 mPa·s.

FIG. 10 of the attached drawings shows Example 4 before treatment, FIG.11 shows Example 4 after convection treatment and FIG. 12 shows Example4 after microwave treatment.

FIG. 10 illustrates that prior to the convection treatment, the ink wasnon-Newtonian and exhibited shear thinning, with a high shear viscosityof 5.84 mPa·s. FIG. 11 illustrates the same ink after the convectiontreatment. It now exhibits a significant reduction in non-Newtonian flowbehaviour or yield viscosity, with a high shear viscosity of 3.42 mPa·s.FIG. 12 illustrates the same ink after microwave heat treatment. It nowalso exhibits a significant reduction in non-Newtonian behaviour oryield viscosity, with a high shear viscosity of 3.67 mPa·s.

FIG. 13 of the attached drawings shows Example 5 before treatment, FIG.14 shows Example 5 after convection treatment and FIG. 15 shows Example5 after microwave treatment.

FIG. 13 illustrates that prior to the convection treatment, the tonerwas non-Newtonian and exhibited shear thinning, with a high shearviscosity of 415 mPa·s. FIG. 14 illustrates the same toner after theconvection treatment. It now exhibits a significant reduction innon-Newtonian flow behaviour or yield viscosity, with a high shearviscosity of 275 mPa·s. FIG. 15 illustrates the same toner aftermicrowave heat treatment. It now also exhibits a significant reductionin non-Newtonian behaviour or yield viscosity, with a high shearviscosity of 304 mPa·s.

Dispersion Stability

All the Examples were examined before and after treatment for dispersionstability by assessment of agglomeration and sedimentation over aspecified time period. Sedimentation was assessed by samples beingplaced in a volumetrically graduated sedimentation flask and the percentof sedimentation analysed after a defined time period; the amount ofdecrease in the meniscus represents the separated (sedimented) solidscompared to the original meniscus volume. Agglomeration was assessed bysamples being placed in a beaker for a specified period of time and thenassessed by stirring samples gently. The agglomeration level can bedetermined by the sample's resistance to stirring.

It was found that over a 6 month storage period, dispersion stabilityhad been greatly improved with the treated samples, as can be seen inthe following results:

Sedimentation Agglomeration Example 1 No treatment >31% moderateConvection Treatment <4% none Microwave Treatment <5% none Example 2 Notreatment >22% moderate Convection Treatment <2% none MicrowaveTreatment <3% none Example 3 No treatment >28% moderate ConvectionTreatment <3% none Microwave Treatment <3% none Example 4 Notreatment >50% moderate Convection Treatment <10% none MicrowaveTreatment <15% minor Example 5 No treatment >25% moderate ConvectionTreatment <3% none Microwave Treatment <5% none

Electrical Characteristics

It is well known that the electrical properties of liquid toners andelectrostatic ink jet inks significantly influence the quality of aprinted image; the most important electrical characteristics ofconventional marking liquids are known to be conductivity,electrophoretic mobility and zeta-potential. Measurement of these aswell as other electrical characteristics of the Examples both prior toand post treatment show improved characteristics which are reflected inthe improved toner performance in respective imaging systems. Theelectrical characteristics of the marking liquids were measured using atoner characterization cell as disclosed in U.S. Pat. No. 6,613,209 toOzerov.

Results were as follows:

No Convection Microwave Treatment Treatment Treatment Example 1 Mobility(m²V⁻¹s⁻¹) 7.0 × 10⁻¹¹ 2.4 × 10⁻¹⁰ 2.7 × 10⁻¹⁰ Conductivity (pS/cm)313.8 389.5 395.2 Zeta Potential (mV) 42 145 163 Example 2 Mobility(m²V⁻¹s⁻¹) 1.8 × 10⁻¹¹ 6.0 × 10⁻¹¹ 6.8 × 10⁻¹¹ Conductivity (pS/cm) 0.2322.7 24.2 Zeta Potential (mV) 53 180 203 Example 3 Mobility (m²V⁻¹s⁻¹)5.7 × 10⁻¹¹ 1.7 × 10⁻¹⁰ 1.9 × 10⁻¹⁰ Conductivity (pS/cm) 0.06 10.0 10.9Zeta Potential (mV) 68 204 228 Example 4 Mobility (m²V⁻¹s⁻¹) 2.5 × 10⁻¹⁰8.1 × 10⁻¹⁰ 6.1 × 10⁻¹⁰ Conductivity (pS/cm) 407 1974 1852 ZetaPotential (mV) 17 55 41 Example 5 Mobility (m²V⁻¹s⁻¹) 4.4 × 10⁻¹² 1.5 ×10⁻¹¹ 1.7 × 10⁻¹¹ Conductivity (pS/cm) 0.07 8.2 7.6 Zeta Potential (mV)52 179 201

Print Testing

The samples were tested for image optical density and backgroundstaining using an electrostatic printer of the type generally disclosedin U.S. Pat. No. 6,167,225 to Sasaki et al. Print samples for Example 4were tested for optical density and background staining using an ink jetprinter of the type generally disclosed in U.S. Pat. No. 6,260,954 toLima-Marques. Image density and background staining measurements weretaken using a Gretag D186 Densitometer made by Gretag, Switzerland.

The results were as follows:

Convection Microwave No Treatment Treatment Treatment Example 1 Image(ODU) 1.25 1.85 1.76 Background (ODU) 0.07 0.00 0.00 Example 2 Image(ODU) 1.32 2.02 1.96 Background (ODU) 0.04 0.00 0.00 Example 3 Image(ODU) 1.22 1.73 1.72 Background (ODU) 0.08 0.00 0.00 Example 4 Image(ODU) 1.42 1.79 1.71 Background (ODU) 0.03 0.00 0.00 Example 5 Image(ODU) 1.30 1.65 1.59 Background (ODU) 0.00 0.00 0.00

As can be seen from the above results, treatment resulted insignificantly increased optical density in print sample image areas, aswell as decreased or no staining or background scatter in non-imageareas.

There has been hereto described a novel method of preparation of markingliquids exhibiting substantially improved imaging performance, includingphysical as well as electrical stability. The instant invention alsodescribes a method by which prior art electrostatic marking liquids witha compatible resin system can be substantially enhanced in imagingperformance, including physical as well as electrical stability byapplication of the present invention.

It can be appreciated that changes to any of the above embodiments canbe made without departing from the scope of the present invention andthat other variations can be made by those skilled in the art withoutdeparting from the invention as defined in the appended claims.

1. A liquid electrostatographic toner or liquid ink jet ink prepared bya method including the steps of, a) preparing a resin system comprisinga resin or resins with optionally a colorant, b) coarse grinding theresin system, c) milling the coarse ground resin system with a carrierliquid to produce a liquid marking particle mix, d) heating the liquidmarking particle mix to a temperature about or greater than the firstsoftening point of the resin system of the marking particle mix to lessthan about the second softening point of the resin system, e)maintaining the temperature of the heated marking particle mix for aselected period of time, f) cooling the marking particle mix to roomtemperature, and g) mixing the marking particle mix with high shear. 2.A liquid electrostatographic toner or liquid ink jet ink as in claim 1wherein the resin system comprises; 0 to 60% of the colourant; and resinor resins to 100%
 3. A liquid electrostatographic toner or liquid inkjet ink as in claim 2 wherein the resin system further comprises aplasticiser in a range of from 0 to 20%.
 4. A liquid electrostatographictoner or liquid ink jet ink as in claim 1 comprising: 1 to 60 percentmarking particle mix by weight, 0.01 to 5 percent charge control agent,0.1 to 20 percent dispersion agent, and carrier liquid to 100 percent.5. A liquid electrostatographic toner or liquid ink jet ink as in claim1 wherein the selected period of time is from several minutes to severaldays depending upon the type of heating applied and the method ofapplying that heat.
 6. A liquid electrostatographic toner or liquid inkjet ink as in claim 1 wherein the heating is provided by convection,conduction or radiation.
 7. A liquid electrostatographic toner or liquidink jet ink as in claim 3 wherein the plasticiser is selected from thegroup comprising sulfonamides, adipates, sebacates and phthalates.
 8. Aliquid electrostatographic toner or liquid ink jet ink as in claim 1wherein the step of milling the resin system includes milling withadditives selected from one or both of the group comprising chargecontrol agents and dispersion agents.
 9. A liquid electrostatographictoner or liquid ink jet ink as in claim 1 wherein the resin is selectedfrom one or more of the group comprising ethyl cellulose, oil modifiedalkyd resin, acrylic ester resin, methacrylic ester resin, polystyrene,silicone-acryl copolymer, silicone resin, silicone-(meth)acrylcopolymer, block polymer or graft polymer, polyolefin copolymer,poly(vinyl chloride) resin, chlorinated polypropylene, polyamide resin,coumarone-indene resin, rosin-modified resin, alkylphenol-modifiedxylene resin, synthetic polyesters; polypropylene or modifiedpolypropylene; alkylated poly vinyl pyrrolidones; natural waxes, montanwax, candelilla wax, sugar cane wax, beeswax; natural resins, ester gumand hardened rosin; natural-resin-modified cured resins, naturalresin-modified maleic acid resins, natural resin-modified phenol resins,natural resin-modified polyester resins, natural resin-modifiedpentaerythritol resins and epoxy resins.
 10. A liquidelectrostatographic toner or liquid ink jet ink as in claim 1 whereinthe colourant when present is selected from one or more of inorganicpigments selected from carbon blacks, silica, alumina, titanium dioxide,magnetic iron oxide, or organic pigments selected from phthalocyanineblue, alkali and reflex blue, phthalocyanine green, diarylide yellow,arylamide yellow, azo and diazo yellow, azo red, rubine toner,quinacridone red, basic dye complexes, lake red, or fluorescent pigmentsand dyestuffs selected from basic dyes and spirit soluble dyes orcombinations thereof.
 11. A liquid electrostatographic toner or liquidink jet ink as in claim 1 wherein the carrier liquid is selected fromthe group comprising isoparaffinic-hydrocarbons, silicone fluids ofstraight chained configuration, silicone fluids of cyclic configuration,silicone fluid of branched configuration, vegetable oils, synthetic oilsor polybutenes or blends thereof.
 12. A liquid electrostatographic toneror liquid ink jet ink as in claim 4 wherein the charge control agent isselected from the group comprising metallic soaps, fatty acids,lecithin, organic phosphorus compounds, succinimides andsulphosuccinates.
 13. A liquid electrostatographic toner or liquid inkjet ink as in claim 4 wherein the dispersion agent is selected from thegroup comprising polymeric hyperdispersants, amino-silicones, polymericpetroleum additives, polymeric oil additives and multi-functionalpigment dispersing agents.
 14. A liquid electrostatographic toner orliquid ink jet ink prepared by a method including the steps of, a)preparing a resin system comprising a resin or resins with a colorantand a plasticiser, the resin system comprising; 1 to 60% of thecolourant; 1 to 20% plasticiser; and resin or resins to 100% b) coarsegrinding the resin system, c) milling the coarse ground resin systemwith a carrier liquid to produce a liquid marking particle mix, d)heating the liquid marking particle mix to a temperature about orgreater than the first softening point of the resin system of themarking particle mix to less than about the second softening point ofthe resin system, e) maintaining the temperature of the heated markingparticle mix for a selected period of time, f) cooling the markingparticle mix to room temperature, and g) mixing the marking particle mixwith high shear; wherein the liquid electrostatographic toner or liquidink jet ink comprises; 1 to 60 percent marking particle mix by weight,0.01 to 5 percent charge control agent, 0.1 to 20 percent dispersionagent, and carrier liquid to 100 percent.